Conventional golf balls can be divided into two general types or groups: solid balls or wound balls. The difference in play characteristics resulting from these different types of constructions can be quite significant.
Solid balls with a two-piece construction are generally most popular with the average recreational golfer, because they provide a very durable ball while also providing maximum distance. Two piece solid balls are made with a single solid core, usually made of a crosslinked rubber, which is encased by a hard cover material. The combination of the core and cover materials, which are very rigid, provide a "hard" feel for the ball when it is struck with a club and provide a ball that is virtually indestructible by golfers. This combination of materials imparts a high initial velocity to the ball, which results in improved distance. In addition, due to this combination these balls have a relatively low spin rate which provides greater distance.
At the present time, the wound ball remains the preferred ball of the more advanced players due to its spin and feel characteristics. Wound balls typically have either a solid rubber or fluid-filled center around which many yards of a stretched elastic thread or yam are wrapped to form a wound core. The wound core is then covered with a durable cover material, such as a SURLYN.RTM. or similar material, or a softer "performance" cover, such as balata or polyurethane. The cover material adheres to the wound core.
Typically, a single strand of thread is employed in forming the wound core. This thread can be wrapped at variable tension as disclosed in U.S. Pat. No. 4,783,078 issued to Giza. However, some balls have used two different threads of different dimensions to form the wound core. In this case, the inner most thread may be wound at a different tension and with a different pattern than the outer most thread. Furthermore, the outer most thread is generally wound in a more open pattern to form larger gaps between the thread to assure good amalgamation between the cover and the wound core.
The United States Golf Association (USGA), the organization that sets the rules of golf in the United States, has instituted a rule that prohibits the competitive use in any USGA sanctioned event of a golf ball that can achieve an initial velocity of 76.2 meters per second (m/s), or 250 ft/s, when tested in a standardized device operated by the USGA (referred to hereinafter as "the USGA test"). However, an allowed tolerance of 2 percent permits manufacturers to produce golf balls that achieve an initial velocity of up to 77.7 m/s (255 ft/s).
Players generally seek a golf ball that delivers maximum distance, which requires a high initial velocity upon impact. Therefore, in an effort to meet the demands of the marketplace, manufacturers strive to produce golf balls with initial velocities in the USGA test that approximate the USGA maximum of 77.7 m/s or 255 ft/s as closely as possible. Manufacturers try to provide these balls with a range of different properties and characteristics, such as spin and compression.
To meet the needs of golfers having varying levels of skill, golf ball manufacturers are also concerned with varying the compression of the ball, which is a measurement of the deformation of a golf ball under a fixed load. A ball with a higher compression feels harder than a ball of lower compression. With initial velocities in the range of 245 to 255 ft/sec in the USGA test, wound golf balls generally have a lower compression which is preferred by better players. Whether wound or solid, all golf balls become more resilient (i.e., have higher initial velocities) as compression increases. Manufacturers of both wound and solid construction golf balls must balance the requirement of higher initial velocity from higher compression with the desire for a softer feel from lower compression.
Wound balls generally have lower compression. Thus, wound balls are softer and provide more spin than solid balls. These characteristics enable a skilled golfer to have more control over the ball's flight and final position. Particularly, with approach shots into the green, the high spin rate of soft covered wound balls enables the golfer to stop the ball very near its landing position. However, soft covered wound balls with their lower compression exhibit a lower initial velocity than hard covered solid balls. This in combination with a higher spin rate than solid balls means wound balls generally display shorter distance than hard covered solid balls. However, the advantages of wound constructions over solid ones are more related to targeting or accuracy than distance.
A softer feel is the result of a lower compression, but feel is also affected by cover hardness and thickness. In wound constructions, a thinner cover will have a softer feel, so manufacturers strive to produce balls with the thinnest possible covers. The cover of a wound ball includes two distinct portions, which are the surface portion and the inner portion. The surface portion consists entirely of cover material. The inner portion is in contact with the wound core, and is essentially an amalgam of cover and windings. This cover inner portion is formed as the cover penetrates the windings during the cover molding process and displaces the air trapped in the wound core. The density of the windings affects the thickness of the cover inner portion, but factors related to the cover will also affect this thickness. Using techniques unique to each cover molding method, manufacturers control the depth to which the cover material penetrates the wound core, and thus the thickness of the cover inner portion. In compression molding, the cover melt flow index, mold temperature and pressures control the thickness of cover inner portion.
One purpose of dipping a wound core in a light latex material is to control the thickness of the cover inner portion. Another purpose of a light latex material is to prevent the wound core from unwrapping prior to it being covered, which would result in an un-playable ball. For example, in balls whose covers are formed in a liquid casting process such as U.S. Pat. Nos. 5,006,297 and 5,733,428, the conventional wound cores are treated by submersion in a light latex material prior to covering. "Light" latex material is one with a particular combination of percentage solids applied using a particular submersion time. For a light latex material, the greater the percentage of solids, the shorter the submersion time, and when the percentage of solids decreases the submersion time increases. For example, a light latex material is formed of about 5% solids applied using a submersion time of less than eight seconds, as disclosed in U.S. Pat. No. 5,006,297. Also, light latex material as disclosed in U.S. Pat. No. 5,733,428 is one formed of about 30%-60% solids and applied using a submersion time of less than eight seconds. A "heavier" latex application on the outer surface of the wound core reduces the amalgamation of the cover with the windings. Thus, an excessive application of latex on the outer surface of the wound core interferes with core-cover adhesion decreasing cover durability.
Another purpose of this light latex material is to seal in any air trapped between the innermost threads. If the air is not trapped, it can rise to the surface of the cover during the covering process and form air bubbles. Since these air bubbles are visible through the cover, they are undesirable imperfections in the cover. However, as discussed above, a heavier application of the latex material can be problematic, for example, it can decrease adhesion of the cover material to the wound core.
Golf ball manufacturers are continually searching for new ways in which to provide wound golf balls that deliver the maximum performance for golfers. It would be advantageous to provide such a wound golf ball with good cover adhesion. The present invention provides such a wound golf ball.